rust/src/test/run-pass/option-unwrap.rs

// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#![feature(unsafe_destructor)]

use std::cell::Cell;
use std::gc::{GC, Gc};

struct dtor {
    x: Gc<Cell<int>>,
}

#[unsafe_destructor]
impl Drop for dtor {
    fn drop(&mut self) {
        // abuse access to shared mutable state to write this code
        self.x.set(self.x.get() - 1);
    }
}

fn unwrap<T>(o: Option<T>) -> T {
    match o {
      Some(v) => v,
      None => fail!()
    }
}

pub fn main() {
    let x = box(GC) Cell::new(1);

    {
        let b = Some(dtor { x:x });
        let _c = unwrap(b);
    }

    assert_eq!(x.get(), 0);
}